Switched-mode power supply (SMPS) systems are widely used in many electronic applications from computers to automobiles. Generally, output voltages within SMPS systems are generated by performing a DC-DC, DC-AC, and/or AC-DC conversion by operating a switch coupled to an inductor or a transformer. Many SMPS systems use high value capacitors as an output load. The SMPS systems with inductors in series with high value output capacitors may cause high voltage and high current spikes during first turn-on.
When designing a SMPS system, various design attributes may be taken into account, for example, efficiency, power, and start-up control. An in-rush current during a start-up of the SMPS system may also be considered. The in-rush current is known as a peak instantaneous current that is caused by an output capacitor acting as short circuit when a power supply is first turned on. The input voltage of the SMPS system may drop significantly if a large current is drawn from the input voltage in a short amount of time and may cause the power supply to reset or prevent the power supply from starting up. A start-up circuit may be used in the SMPS system to reduce such in-rush current conditions, as well as prevent and avoid various overvoltage and/or overcurrent conditions during the start-up.